Fruit yield of virus-resistant transgenic summer squash in simulated commercial plantings under conditions of high disease pressure

Abstract

Fruit yield of transgenic crookneck summer squash ZW-20 resistant to Zucchini yellow mosaic virus
(ZYMV) and Watermelon mosaic virus (WMV) and of a susceptible nontransgenic lineage of the same
genotype was compared over two consecutive years. Field trials relied on small-scale plantings that
reflected commercial settings under conditions of severe disease pressure by ZYMV and WMV with
infection achieved via aphid-mediated inoculation from virus source border plants. Across all trials, all
transgenic plants were highly resistant to ZYMV and WMV, and the majority (79%, 331 of 421) produced
3 to 9 fruits per plant. In contrast, all control plants had severe systemic symptoms and the majority
(80%, 336 of 421) produced 0 to 4 fruits per plant. In addition, all fruits of transgenic squash ZW-20H and
ZW-20B were of marketable quality whereas most fruits of nontransgenic controls (96%, 947 of 989)
were unmarketable. Differences in fruit number (P = 0.0001) and fruit weight (P = 0.0001) between
transgenic and conventional squash plants were significant but not between ZW-20H and ZW-20B plants
(P = 0.933 and P = 0.964, respectively). This is the first report on a comparative analysis of fruit yield of
transgenic versus conventional summer squash under conditions approaching commercial plantings in
which high infection rates of ZYMV and WMV were achieved via indigenous aphid populations.